Various types of knitting elements are used in knitting machines which may be of the flat-bed or circular machine type. Typical elements are described, for example, in German Pat. No. 28 20 925 to which U.S. Pat. No. 4,452,053, Egbers et al, corresponds and German Patent Disclosure Document DE-OS 30 14 751.
It is a continuous endeavor to increase the operating speed of knitting machines. The head portions of the knitting elements which are engaged by the knitting yarn or threads are increasingly stressed, and the heads, and especially hook portions thereof then tend to break. In order to prevent such breakage, and to increase the lifetime and operating duration of the knitting elements, it has been proposed to couple the foot or butt portion of the respective knitting elements with the head portion by a section which is somewhat resilient. Consequently, the shaft of the knitting element is sometimes made to be resilient or has a somewhat resilient portion to permit the entire element to vibrate or oscillate with damped vibrations and oscillations. The impact energy applied to the foot or butt portion of the knitting element can thus be absorbed and transferred into bending forces in the element itself. One arrangement of this type is described in U.S. Pat. No. 4,452,053, in which an intermediate portion is located between the head end and the foot or butt end of a knitting needle, which intermediate portion has a length of at least 8 mm and a width of at the most 1.1 mm. Increasing the width of the strip or rib formed thereby, and increasing the length of this low-dimensioned strip decreases the tendency of the needle to break at the head or hook portion thereof.
It is not possible, unfortunately, to decrease the width of the strip and increase its length too much since the stability of the knitting element otherwise will be impaired. In order to increase the stability of knitting tools, it has been proposed (see German Pat. No. 30 14 751) to provide two ribs, one of which has a width of at the most 1.1 mm and, further, a lower rib of the same width or a lesser width. A free space or hole will then be defined between the respective ribs which may be subdivided by a connecting piece. The length of this free space, subdivided or not, is at least 8 mm.
Limits are placed on the increase in needle operating speed by reduction of the width of the respective connecting strips. These elements, which are all made by punching, have the characteristics that head or hook breakage is decreased; yet, as the shaft portion is reduced in effective cross section, the danger of breakage of the shaft increases. The decrease in head breakage, thus, will result in an increase in shaft breakage and a suitable compromise or balance must be found.
Investigation of the forces acting on the knitting tools, for example knitting needles, have shown that the forces stress the needle butt by applying blow-like pulse thereagainst which will be transferred into bending forces in the resilient, bendable portions of low width within the needle. These bendable portions will transfer the bending forces into bending oscillations which have amplitude excursions deviating from the plane of symmetry of the respective knitting element. The rapidly occurring impacts acting on the needle butt may become additive in the vibrations or oscillations of the needle so that the material of the needle will be subjected to fatigue which leads to breakage of the needle shaft or shank. The oscillations imposed by the impacts due to the cams acting on the needle may modulate each other, and may be in phase synchronism, or may be phase-shifted. Under some operating conditions, the superimposed oscillations may so occur, in time, with respect to each other that a substantial portion of the impact energy is transferred to the hook portion or head portion of the knitting element, and hence, again, leads to premature destruction thereof.
It has been proposed--see Japanese Utility Model 57/9433--to punch an opening in the shaft of latch knitting needles which, otherwise, is solid and extends from the needle head to the butt or foot end thereof. The opening may extend up to the back side of the shaft, and is filled with material absorbing vibration, such as a plastic or the like. The vibration-absorbing material extends beyond the side surfaces of the needle shaft or needle shank. The entire shaft or shank is massive. The purpose of this arrangement is to constrain transverse movement of the needle within the needle groove and to prevent slithering movement of the needle which may be caused by impacts applied to the needle foot or butt end. The vibration-absorbing material, extending laterally over the sides of the needle shaft, and engaging in the surfaces defining the needle groove, then, will prevent such lateral vibration. A needle with a massive needle shaft, retained snugly in the groove by a plastic insert, cannot be operated and is not comparable to a needle made as a punched element which has its shaft reduced to the small width of about 1.1 mm to form a highly resilient portion therein. The massive shaft with the plastic insert provides little resiliency along a dimension at right angles to the longitudinal extent of the needle, that is, permitting bending excursions in the plane of the needle shaft itself.